🛡️ Sentinel: [CRITICAL] Fix SQL injection vulnerability in metadata generator

[thebearwithabite]

🚨 Severity: CRITICAL
💡 Vulnerability: SQL injection vulnerability in metadata_generator.py via untrusted dictionary keys passed to save_file_metadata and injected directly into query strings.
🎯 Impact: Attackers could inject arbitrary SQL to modify schemas or drop tables (e.g., column name injection).
🔧 Fix: Fetched schema with PRAGMA table_info and filtered metadata keys against this explicitly allowlisted set before building the dynamic INSERT query.
✅ Verification: Tested via a mock script executing a drop table payload, verified table persistence and column sanitization. All unit tests successfully executed.

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PR created automatically by Jules for task 12165267220019104563 started by @thebearwithabite

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